1. Field of Invention
This invention relates to spinal cord stimulation (SCS) devices, specifically to a component system which, when “added on” to existing (or future) SCS devices, will greatly enhance these SCS devices by automatically monitoring, measuring, and classifying a patient's levels of discomfort, automatically generating the most appropriate “programs” or “therapies” to relieve the patient's pain, and automatically self-adapting itself to changes within the patient over time.
2. Prior Art
More than 20 years ago, electrical stimulation of the spinal cord or “dorsal column stimulation” was introduced in the treatment of chronic pain. This approach is called spinal cord stimulation (SCS). SCS works by blocking pain signals from being received by the brain through the surgical insertion of electrodes along different points of the spinal cord. SCS therapies use precise, low-voltage electrical stimulation through one or two carefully placed insulated leads in the spinal cord. Trial-and-error is used to find the optimal combination of signals in a program that would eliminate or at least mitigate the pain.
Since my invention will serve as an add-on to existing (or future) implantable devices that target the spinal cord stimulation pain market, I offer a comprehensive overview of existing device technology and components.
A spinal cord stimulation system uses several components for relieving chronic, intractable pain in the cervical area, the trunk and/or limbs, and the legs and/or feet. It applies precisely controlled low-voltage electrical stimulation to the spinal cord through one or two carefully placed insulated leads. The surgical procedure involves the insertion of a compact implantable pulse generator (IPG) in the lower anterior abdomen wall that is connected to a strip of electrodes implanted adjacent to the back part of the spinal cord. The leads are implanted near the spinal nerves that correspond to the patient's pain areas. Through low-voltage electrical stimulation of these electrodes, the normal pain signals that travel in the posterior part of the spinal cord are blocked, providing partial or complete pain relief.
Apart from the electrodes, the system includes an implantable pulse generator in an area agreed to by the patient, and an external remote device worn on the patient's belt. The remote control device sends signals to the implantable pulse generator, stimulating the spinal cord via the leads. In this way, messages of pain are prevented from reaching the thalamus in the brain. As a result, the patient feels a “tingling” sensation called paraesthesia, instead of pain.
A spinal cord stimulator (SCS) system for pain relief contains a remote control device programmed by a small computer, an antenna, an implantable pulse generator, and epidural multi-electrode leads which offer a better choice of stimulation combinations. The implantable pulse generator and the epidural electrodes are connected through subcutaneous lead wires.
The implantable pulse generator is surgically implanted, usually in the patient's abdominal area and tunneled under the skin to connect the leads and extensions, such as the wires. The implantable pulse generator receives electrical pulses from the remote control device and sends them to the spinal cord or, in some cases, to a peripheral nerve to control the patient's pain. The implantable pulse generator has permanently attached extensions that connect to the leads. It is a pulse generator that delivers adjustable signals. One can tune 3 different parameters: Pulse width (from 10 to 500 micro seconds), Frequency (10 to 1500 Hz), and Amplitude (0.1V to 12.0V). Typically, the starting pulse width parameter is between 150 and 500 microseconds for pain located in the thoracic area, and between 50 and 250 microseconds for pain located in the cervical area. The amplitude should always be kept as low as possible in order to preserve battery life.
Each lead is implanted in the epidural space next to the spinal cord at a spot that corresponds to the patient's pain (between the C2 and L1 vertebra levels). They are placed so that the patient feels “tingling” instead of pain in the part(s) of the body being stimulated. The electrodes at the tip of each lead carry the electrical impulses to the spinal nerves, creating a tingling feeling rather than the sensation of pain.
A lead consists of one or more contacts encased in one implanted structure. A contact or electrode is the basic stimulation component that represents one of the poles of the current flow. A lead is typically around a 1.5 to 2 mm diameter catheter 60 cm long. Each lead contains 4 to 8 controllable contacts. Since electrical current flows between a positive pole and a negative pole, there must be at least one anode and one cathode electrode in order to cause any stimulation. Sometimes a positive electrical stimulation is needed, and sometimes a negative stimulation is better. Not all electrodes need to be active. Thus, there is an additional polarity “state” termed “off” (the electrode polarity is zero (0)). With this amount of electrodes, the number of possible electrode polarity combinations (3 per electrode negative, positive and neutral) can reach 316, which equals 43,046,721 (for 16 electrodes—8 electrodes on each lead). Once the physician defines exactly what areas of the body needs treatment, he or she has to set the optimal stimulation settings by determining the best polarity combinations. This is very difficult to achieve. The only way to accomplish this is through experimentation and previous physician expertise.
The programming information for the SCS system are provided by and downloaded from an external remote device. The clinician uses this remote control device to set stimulation parameters. The remote control device produces a signal that sends programs that are transmitted through the skin via an attached antenna positioned over the implantable pulse generator. A major advantage of this system is that the remote control device can be customized through a computer driven interface.
The stimulation parameters (electrical signal parameters, and contact polarity), as well as the leads placement, are set and adjusted through hardware/software programming consoles. The hardware consists of a portable computer that can be connected to the remote control device.
It is important to note that spinal cord stimulator (SCS) devices and other implantable tissue stimulator systems come in two general types: radiofrequency (RF) controlled and fully implanted like the implantable pulse generator (IPG)—based devices described above.
The fully implanted (IPG) type of stimulating system contains the programmable stimulation information in memory, as well as a power supply, e.g., a battery, all within the implanted pulse generator, or “implant”, so that once programmed and turned on, the implant can operate independently of external hardware. The implant is turned on and off and programmed to generate the desired stimulation pulses from an external programming device using transcutaneous electromagnetic, or RF links. Such stimulation parameters include, e.g., the pulse width, pulse amplitude, repetition rate, and burst rates.
The second type of stimulating system, commonly referred to as an “RF” system, includes an external transmitter inductively coupled via an electromagnetic link to an implanted receiver that is connected to a lead with one or more electrodes for stimulating the tissue. The power source, e.g., a battery, for powering the implanted receiver-stimulator as well as the control circuitry to command the implant is maintained in the external unit, a hand-held sized device that is typically worn on the patient's belt or carried in a pocket. The data/power signals are transcutaneously coupled from a cable-connected transmission coil placed over the implanted receiver-stimulator device. The implanted receiver-stimulator device receives the signal and generates the stimulation. The external device usually has some patient control over selected stimulating parameters, and can be programmed from a physician programming system.
My invention is not limited to working with implantable pulse generator based spinal cord stimulators. It also works perfectly with radiofrequency (RF) based spinal cord stimulators. The advantage of radiofrequency type SCS devices is that the battery can be easily changed or recharged. Previously, radiofrequency SCS systems would have been better suited for patients with more complicated pain patterns, which require more energy and programming. However, the development of rechargeable batteries for implantable pulse generator SCS systems very recently means that implantable pulse generator SCS systems are not at a disadvantage in this regard any longer.
Programs are generally composed of different modules that address all the various aspects of SCS, including patient management, billing, patient testing, and analysis of the implanted stimulator and the stimulation patterns. Based on information provided by the patient on the pain characteristics and patterns, the software makes suggestions as to the optimal electrode placement. The patient enters this information through a graphical interface by drawing the pain area on the screen (map of the body) using a pen. The pain intensity and the critical areas are also given. Once the electrodes are implanted, the program can be downloaded into the radio receiver and the electrical parameters can be modified. The information obtained through a patient-interactive module is then recorded in a database.
Current SCS device technology is outdated, unintelligent, inconvenient, and inefficient. Patient program settings are based on “trial and error” approaches and patient “hunches.” Setting, programming, and tuning SCS devices is largely manual, and is very time consuming for physicians and patients alike. Current SCS devices cannot adjust stimulation based upon real-time patient physiological parameters and changes. The only way SCS programs can be updated/changed is by a physician's intervention.
The main drawback of such existing systems is that they do not contain any intelligence or facility to determine the most appropriate electrode combinations (contact polarization) and electrical parameters. This is currently done manually through a tedious and non-deterministic interactive process with the patient. A few days after surgery, the physician will provide the patient with a set of programs loaded in the implantable pulse generator. These programs (position of the contacts and parameters of the electrical signal) are determined from the patient oral feedbacks. The patient then returns home and evaluates them for several weeks in order to give the physician some additional feedback. Then, during subsequent follow-up visits, the physician will erase some programs, and slightly modify others to provide the most appropriate settings for the patient. The whole procedure is very long, and very costly.
One of the key factors for successful electrical stimulation therapy is the accurate settings of electrical parameters.1 The optimal parameters are based on the evaluation of three physiological variables elicited by electrical stimulation of the intra-spinal structures: the paraesthesia response, the perception intensity and the usage range. 1 Barolat G., Zeme S., Ketcik B., “Multifactorial analysis of epidural spinal cord stimulation”, Stereotact Funct Neurosurg 1991; 56:77-103.
It is essential for the patient to experience paraesthesia, a pleasant tingling sensation in the painful area during the stimulation. In clinical applications, electrical stimulation starts with the lowest intensity of current (ideally with 0 mA), and it is then gradually increased until the patient feels a slight tingling.
The first response by the patient is called “stimulation perception threshold”. After the determination of the perception threshold, the intensity is slowly increased again. When the maximal bearable level of stimulation is reached, the patient may feel painful muscle contractions. This level of intensity corresponds to the “tolerance threshold”. The patient tolerance is critical, particularly if unpleasant sensations are felt just over the perception threshold or if they occur before sufficient intensity has been reached to achieve paraesthesia.
Adjustable electrical parameters, including amplitude, pulse width, frequency, polarity (contact configuration), and pulse modulation, are available in the clinically used SCS devices.2 There are many publications in the present literature reporting the clinical results of SCS therapy applications.3 However, only a few published studies involving the systematic analysis of perception intensities have focused on the optimal parameters to achieve successful spinal cord stimulation.4 Research studies revealed that the output of a spinal cord stimulator must not exceed 10V (10 mA), and the majority (70%) required treatment levels of less than 5V (5 mA). No previous study has addressed the question of how electrode location and contact configuration affect the perception intensity of stimulation. 2 Barolat G., Massaro F., He J., Zeme S., Ketcik B., “Mapping of sensory responses to epidural stimulation of the intraspinal neural structures”, in man. J neurosurg 1993, 78:233-239. North RB., Ewend M G., Lawton M T., Piantadosi S., “Spinal cord stimulation for chronic intractable pain: Superiority of multichannel devices”, Pain 1991; 44:119-130. North R B., Ewend M G., Lawton M T., Piantadosi S., “Spinal cord stimulation for chronic intractable pain: Superiority of multichannel devices”, Pain 1991; 44:119-130.3 Long D M., Erickson D., “Stimulation of the posterior columns of the spinal cord for relief of intractable pain”, Surg Neurol 1975; 4:134-142. Meglio M., Cioni B., Rossi G F., “Spinal cord stimulation in management of chronic pain”, J Neurosurg 1989; 70:519-524. Augustinsson L E., Carlsson C A., Holm J., Jivegard L., “Epidural electrical stimulation in severe limb ischemia”, Ann Surg 1985; 202:104-110. Jacobs M J., Jorning P J., Beckers R C., Ubbink D T., Van Kleef M., Slaaf D W., Reneman R S., “Foot salvage and improvement of microvascular blood flow as a result of epidural spinal cord electrical stimulation”, J Vasc Surg 1990; 12:354-360. Dimitrijevic M., “Neurophysiological evaluation and epidural stimulation in chronic spinal cord injury patients”, in Kao C C., Bunge R P., Reier P J (eds): Spinal Cord Reconstruction. New York, Raven Press, 1983, pp. 465-474. Barolat G., Myklebust J B., Hemmy D C., Wenninger W., “Immediate effects of spinal cord stimulation in spinal cord stimulation in spinal spasticity”, J Neurosurg 1985; 62:558-562.4 Tulgar M., New Approaches to Electrical Stimulation of the Nervous System for the Relief of Pain; PhD thesis, University of Liverpool, 1991, chap. 4. Fluks J., Lindemans F W., “Medtronic Itrel Totally Implantable Stimulation System”, Kerkrade, Medtronic BV International Research and Science Centre, 1984.
The configuration process consists of: (a) optimizing the placement of the leads; and (b) finding the right values for the electrical stimulation parameters (programs) to enhance the possibility of obtaining a result that will cover as completely as possible the painful area(s) of the body. At first, the leads must be surgically inserted somewhere along the spinal cord depending on the pain location. Some rules or guidelines5 have been defined as to where approximately one should place the electrodes. The resulting implants often do not lead to exactly the points that are connected with the targeted pain locations. Thus, these locations often need some adjustment based on the patient's reaction. It could be very useful to use a database that contains the experience of successful lead placements in order to automate this task. For the purposes of this invention, however, we will only focus on the second stage: SCS parameter selection and automatic control. 5 Giancarlo Barolat, “Current Status of Epidural Spinal Cord Stimulation”, Neurosurgery quarterly 5(2), pp. 98-124, Raven press Ltd., New York, 1995. Giancarlo Barolat, et. al., “Multifactorial Analysis of Epidural Spinal Cord Stimulation”, Stereotact Funct Neurosurg, Vol. 56, pp. 77-103, 1991. J. Holsheimer, et. al., “Optimum electrode geometry for spinal cord stimulation: the narrow bipole and tripole”, Medical & Biological Engineering & Computing, July 1997.
The settings for all stimulation parameters (contact polarities, frequency, pulse width, amplitude, and contact currents) result in a program that is loaded in the remote control device's memory in order to be transmitted to the implantable pulse generator. The selection of electrode polarities (+, −, 0) is used to “target” a specific pain site. For that specific task, there is some preliminary knowledge that describes what exact polarity combinations and frequency one needs to select to enhance the coverage of the area affected by the pain. For example, in the case of a low-back pain, the leads are usually inserted between areas T8 and T10 of the spinal cord (covered areas are hips, legs, and feet). If one sends a + signal to point No. 1,− signal to point No. 2, and + signal to point No. 3, and no signals to all other points, then this combination of polarities described by the sequence +−+00000 may in most cases result in relief to the hips of the patient. If the pain is caused by motor neurons, one requires a frequency of about 1 Hz; to target pain on other neurons, one needs larger frequencies (˜10-20 Hz).
This is the preliminary knowledge required to generate the first (draft) program. After that, the physician must determine the amplitude. He starts with the smallest possible amplitude that is most probably not perceived by the patient, and increases the amplitude until the patient starts feeling the effect (the “tingling”). The patient must also indicate in which of the zones he has this feeling. If some of these feelings are in undesired zones, some parameters of the programs must be adjusted according to the patient's feedback. If all the feelings are in the desired zones, one may begin increasing the amplitude until the level when the feeling becomes uncomfortable is obtained. For a given program, these two thresholds are marked down, and in the future, amplitudes of using this program must be between these two values.
The primary reasons for this relatively primitive methodology for configuring SCS programs are:    a) a lack of systematic research on the relationship between stimulus and electrode parameters and their clinical effects;    b) insufficient knowledge regarding both the neuronal elements in the spinal cord that are actually stimulated and the elements that have to be stimulated in order to obtain an adequate clinical effect.6     c) And, most importantly, prior to my invention, a complete lack of the required technology advanced enough to allow SCS devices to operate in an automatic, self-adaptive manner. 6 Dimitrijevic M R, Faganel J., Young RR., “Underlying mechanisms of the effects of spinal cord stimulation in motor disorders”, Appl Neurophysiol 1981; 44:133-140. Bantli H., Bloedel J R., Long D M., Thienprasit P., “Distribution of activity in spinal pathways evoked by experimental dorsal column stimulation”, J Neurosurg 1975; 42:290-295. Phillips C G., “Possible modes of action of extradural electrical stimulation on the spinal cord”, Appl Neurophysiol 1981; 44:16-21. Gybels J., Van Roost D., “Spinal cord stimulation for the modification of dystonic and hyperkinetic conditions: A critical review”, in Eccles J., Dimitrijevic M R (eds): Recent Achievements in Restorative Neurology. I. Upper Motor Neuron Functions and Dysfunctions, Basel, Karger, 1985, pp. 56-70.
Some investigations have focused on the neural target elements of SCS. Swiontek et al.7 measured stimulus induced potential distributions in cadaver spinal cords. A theoretical investigation considering the targets of stimulation was initiated by the late Barry Coburn.8 In these studies, a computer model of the electrical properties of the spinal cord and surrounding tissues was used in order to predict which fibers in the spinal cord would be excited by epidural stimulation. In 1986, Holsteimer et. al. started a study using a similar approach to analyze the effects of various geometric parameters and to relate them to clinical data9. 7 Swiontek T J., Sances A., Larson S J., et. al., “Spinal cord implant studies”, IEEE Trans Biomed Eng. 1976, BME-23: 307-312.8 Coburn B., “Electrical stimulation of the spinal cord: Two-dimensional finite element analysis with particular reference to epidural electrodes”, Med Biol Eng Comp 1980, 18:573-584. Sin WK., Coburn B., “Electrical stimulation of the spinal cord: A further analysis relating to anatomical factors and tissue properties”, Med Biol Eng Comp 1983; 21:264-269. Coburn B., Sin W K., “A theoretical study of epidural electrical stimulation of the spinal cord. Part I. Finite element analysis of stimulus fields”, IEEE Trans Biomed Eng 1985; BME-32:971-977. Coburn B., “A theoretical study of epidural electrical stimulation of the spinal cord. Part II. Effects on long myelinated fibers”, IEEE Trans Biomed Eng 1985; BME-32:978-986.9 Holsheimer J., Struijk J J., “Electrode combination and specificity in spinal cord stimulation”, Proc 9th a Int Symp Advances in External Control of Human Extremities, Dubrovnik, 1987, pp. 393-404. Holsheimer J., Struijk J J., “Analysis of spinal cord stimulation. 1. Field potentials calculated for a homogeneous medium; in Walling a W., Boom H B K, de Vries J. (eds): Electrophysiological Kinesilogy, Amsterdam, excerpta Medica Congress Series, 1988, Vol. 804, pp. 95-98. Struijk J J., Holsheimer J., Van Veen B K, et. al., “Analysis of spinal cord stimulation. 11. Simulation of field potentials in an inhomogeneous medium”, in Walling a W., Boom H B K., de Vries J. (eds): Electrophysiological Kinesiology, Amesterdam, Excerpta Medica Congress Series, 1988, Vol. 804, pp. 99-102. Holsheimer J., Struijk J J, “Improvement of methods in spinal cord stimulation”, Int J Rehab Res 1989, 11:409-410. Struijk J J., Holsheimer J., Van Veen BK., Boom H B K., “Epidural spinal cord stimulation: Calculation of field potentials with special reference to dorsal column nerve fibers”, IEEE Trans Biomed Eng 1991; BME-38:104-110.
It is important to note that the described process remains completely manual and incremental, and may not lead to the 3 or 4 best programs for the patient. That is precisely what I would like to automatically obtain when one cannot try all possible options. In the cases that are not covered by “rules”, when one uses a trial-and-error method, there are too many different options. Simply trying them all is not possible. Therefore, one requires intelligent methods for generating the best SCS programs.
Existing SCS devices have demonstrated several deficiencies, especially in terms of cost, convenience, and efficiency:    a) First, it takes too long to determine the optimal set of stimuli to apply to the patient in relation to the large number of possible combinations.    b) Second, each patient is required to visit a physician several times to adjust the system, which can become prohibitively expensive.    c) Third, the selection of the appropriate program and the control of the electric signal parameters—frequency, amplitude, and pulse width—must be done manually by the patient.
In summary, existing SCS devices are not intelligent, they are not self-learning, and they do not provide automatic feedback. Existing SCS devices are not intelligent, self-learning, or automatic because none of the existing technologies which SCS devices utilize are advanced enough.
In fact, there are not even any new patents which purport or claim to automatically adjust a patient's pain treatment levels based upon automatic feedback from actual, specified, physical and/or physiological patient parameters.
Based upon a recent search, we found several related works on neural stimulation for pain control. Most of the patents proposed a straightforward solution without incorporating any automatic feedback loop between the patient and the system.
U.S. Pat. Nos. 4,233,986 and 4,735,204 describe a conventional neural stimulator for pain control where a practitioner, based on patient feedback, manually controls the strength of the signal applied to the electrodes.
U.S. Pat. No. 5,702,426 presents a method to automatically adjust the electrical signal parameters on implantable medical devices. This approach still does not contain any feedback from human physiological parameters as a result of the electrical stimulation.
U.S. Pat. No. 5,913,882 presents neural stimulation techniques to incorporate feedback to control the amplitude of the pulse generator to maintain a more uniform stimulation effect.
U.S. Pat. No. 6,909,917 presents a new method to determine a desired stimulation pattern applied to an electrode or a group of electrodes. The patient or physician uses a friendly user interface to program which group of electrodes will be targeted as well as the current waveform on each contract. Though this patent provides a method to efficiently program an SCS device via a graphical user interface to generate quality stimulation to the patient, there is no automatic detection of pain levels and there is no automatic generation of corresponding appropriate stimulation programs.
U.S. Pat. No. 6,622,048 presents a method to program an implanted SCS through the use of a computer. The computer is connected to the implant device in order to adjust the applied stimuli to each area of perceived pain. The patient or physician communicates with the computer to provide inputs for both the body's area of pain and the resulting area to be covered by the stimulation. The computer uses this information to quickly change the electrode configuration and to generate the appropriate stimulus parameters. This is primarily done by using a database that maps various electrode combinations to both the pain region and the region that is covered by the stimulation. This patent provides no feedback loop and adaptive behavior within the SCS system to enable the SCS system to automatically generate the best stimulation programs once pain is felt by the patient.
U.S. Pat. No. 6,871,099 is a small implantable stimulator that can be located near or within a region of the spinal cord where pain is sensed. This particular stimulator has at least two electrodes to provide the means for stimulating a nerve or tissue when desired. This small stimulator can also work as a closed loop using at least one sensor which will adjust the stimulation parameters based on the sensed coupling condition. This patent proposes a first step toward providing a closed-loop system. However, this invention does not provide true intelligence since it does not understand whether the patient feels pain or not, and, hence, it cannot automatically trigger stimulation with the most appropriate program. In addition, the stimulator is limited to coverage of a small region of the body. The use of this device is limited to stimulation of a single nerve, and, therefore, is incapable of providing patients with the broad spectrum and array of stimulation and pain relief afforded by a spinal cord stimulator system. Moreover, this invention would require several stimulators to be implanted to cover a larger region; hence, it requires much more complicated patient surgery.
U.S. Patent 20030153959 has been recently filed, in 2003. It describes a system based on current SCS technologies, providing automatic adjustment of stimulus output as a function of sensed coupling efficiency. This system is based on a sensor that measures the coupling efficiency of an electrical stimulation applied to neural tissue in order to automatically adjust the appropriate magnitude of stimulating current pulse to the patient. We consider this patent to be a preliminary system towards automatic control of pain.
Our system goes beyond this concept, as it is based on multiple sensors monitoring different aspects of the patient's pain status in order to automatically adjust the correct electric current pulses and find the best contact polarity on the leads in order to provide the patient with the best pain relief possible. One of the major advantages is that our system is capable of auto-configuring itself by learning how the patient will react based on applied stimuli. Our system actually creates an automatic feedback loop using a set of input sensors, analyzes the data (from the data fusion process), generates a diagnostic, and gradually adjusts the right stimulus being applied.
This referenced competitor system (U.S. Patent 20030153959) does not include a self-learning capability within the system to automatically adjust its stimuli. In addition, this competitor system cannot rapidly program the polarity of the electrode points. Moreover, this approach is significantly variant; as such, it does not threaten our patent application.